5-Fluorouracil in Combination with Calcium Carbonate Nanoparticles Loaded with Antioxidant Thymoquinone against Colon Cancer: Synergistically Therapeutic Potential and Underlying Molecular Mechanism

Colon cancer is the third most common cancer worldwide, with high mortality. Adverse side effects and chemoresistance of the first-line chemotherapy 5-fluorouracil (5-FU) have promoted the widespread use of combination therapies. Thymoquinone (TQ) is a natural compound with potent antioxidant activity. Loading antioxidants into nano delivery systems has been a major advance in enhancing their bioavailability to improve clinical application. Hence, this study aimed to prepare the optimal TQ-loaded calcium carbonate nanoparticles (TQ-CaCO₃ NPs) and investigate their therapeutic potential and underlying molecular mechanisms of TQ-CaCO₃ NPs in combination with 5-FU against colon cancer. Firstly, we developed purely aragonite CaCO₃ NPs with a facile mechanical ball-milling method. The pH-sensitive and biocompatible TQ-CaCO₃ NPs with sustained release properties were prepared using the optimal synthesized method (a high-speed homogenizer). The in vitro study revealed that the combination of TQ-CaCO₃ NPs (15 μM) and 5-FU (7.5 μM) inhibited CT26 cell proliferation and migration, induced cell apoptosis and cell cycle arrest in the G₀/G₁ phase, and suppressed the CT26 spheroid growth, exhibiting a synergistic effect. Finally, network pharmacology and molecular docking results indicated the potential targets and crucial signaling pathways of TQ-CaCO₃ NPs in combination with 5-FU against colon cancer. Therefore, TQ-CaCO₃ NPs combined with 5-FU could enhance the anti-colon cancer effects of 5-FU with broader therapeutic targets, warranting further application for colon cancer treatment.